Moros E G, Straube W L, Klein E E, Yousaf M, Myerson R J
Radiation Oncology Center, Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, MO 63110.
Int J Radiat Oncol Biol Phys. 1995 Feb 15;31(4):893-904. doi: 10.1016/0360-3016(94)00469-2.
The feasibility of simultaneously delivering external electron beam radiation and superficial hyperthermia using a scanning ultrasound reflector-array system (SURAS) was experimentally investigated and demonstrated.
A new system uses a scanning reflector to distribute the acoustic energy from a planar ultrasound array over the surface of the target volume. External photon/electron beams can be concurrently delivered with hyperthermia by irradiating through the scanning reflectors. That is, this system enables the acoustic waves and the radiation beams to enter the target volume from the same direction. Reflectors were constructed of air-equivalent materials for maximum acoustic reflection and minimum radiation attenuation. Acoustically, the air reflectors were compared to brass reflectors (assumed ideal) for reflectivity and specular quality using several single transducers ranging in frequency from 0.68 to 4.8 MHz. The relative reflectivity was determined from acoustic power measurements using a force-balance technique. The specular quality was assessed by comparing the acoustic pressure fields reflected by air reflectors with those reflected by brass reflectors. Also, acoustic pressure fields generated by a SURAS prototype for two different arrays (2.24 and 4.5 MHz) were measured to investigate field distribution variations as a function of the distance separating the array and the scanning reflector. All pressure fields were measured with a hydrophone in a degassed water tank. Finally, to determine the effect of the air reflectors on electron dose distributions, these were measured using film in a water-equivalent solid phantom after passage of a 20 MeV electron beam through the SURAS. These measurements were performed with the reflector scanning continuously across the electron beam and at rest within the electron beam.
The measurements performed using single ultrasound transducers showed that the air reflectors had power reflectivities of 87-96% that of brass, and that for smooth surfaces the reflections from air reflectors were as specular as those from brass reflectors. Acoustic pressure fields measurements of the SURAS for two different arrays showed that the 50% pressure amplitude contours were well-distributed across the projected surface area of the array for different distances separating the array and the reflector. Finally, film dosimetry showed that the electron dose distribution was not affected by the air reflector of the SURAS either for the scanning case or the stationary case. This indicates that the reflectors as made are basically water-equivalent in terms of high energy ionizing radiation. The measured isodoses also indicate that the constructed SURAS prototype would allow the delivery of adequate radiation (90% isodose) to a depth of 2.0 cm.
The results presented show that the SURAS design has the potential to deliver hyperthermia to large superficial tumors, while allowing simultaneous irradiation with 20 MeV electron beams without adverse effects on the radiation dose delivery.
通过实验研究并证明了使用扫描超声反射器阵列系统（SURAS）同时进行外部电子束辐射和浅表热疗的可行性。
一种新系统使用扫描反射器将平面超声阵列的声能分布在目标体积表面。外部光子/电子束可通过扫描反射器进行照射，从而与热疗同时进行。也就是说，该系统使声波和辐射束能从同一方向进入目标体积。反射器由空气等效材料制成，以实现最大声反射和最小辐射衰减。在声学方面，使用几个频率范围为0.68至4.8MHz的单个换能器，将空气反射器与黄铜反射器（假定为理想反射器）在反射率和镜面反射质量方面进行比较。相对反射率通过使用力平衡技术进行声功率测量来确定。通过比较空气反射器反射的声压场与黄铜反射器反射的声压场来评估镜面反射质量。此外，测量了SURAS原型针对两种不同阵列（2.24和4.5MHz）产生的声压场，以研究场分布随阵列与扫描反射器之间距离的变化。所有压力场均在脱气水箱中用水听器进行测量。最后，为了确定空气反射器对电子剂量分布的影响，在20MeV电子束穿过SURAS后，使用水等效固体模体中的薄膜进行测量。这些测量是在反射器在电子束上连续扫描以及在电子束内静止的情况下进行的。
使用单个超声换能器进行的测量表明，空气反射器的功率反射率为黄铜反射器的87 - 96%，并且对于光滑表面，空气反射器的反射与黄铜反射器的反射一样具有镜面反射特性。针对两种不同阵列的SURAS声压场测量表明，对于阵列与反射器之间的不同距离，50%压力幅度等值线在阵列的投影表面积上分布良好。最后，薄膜剂量测定表明，无论是扫描情况还是静止情况，电子剂量分布均不受SURAS空气反射器的影响。这表明就高能电离辐射而言，所制作的反射器基本上是水等效的！测量得到的等剂量线还表明，所构建的SURAS原型能够将足够的辐射（90%等剂量）输送到2.0cm的深度。
所呈现的结果表明，SURAS设计有潜力对大型浅表肿瘤进行热疗，同时允许与20MeV电子束同时照射，而不会对辐射剂量输送产生不利影响。
